Add new Sorbet/RedundantExtendTSig cop

[sambostock]

This cop is intended to be used in applications that have monkey patched T::Sig into all modules.

Module.include(T::Sig)

# later
module MyModule
  extend T::Sig
# ^^^^^^^^^^^^^ Do not redundantly `extend T::Sig` when it is already included in all modules.
  sig { void }
  def whatever = nil
end

It is disabled by default, as only application developers themselves can know if it applies to their app.

[sambostock]

Looks like the way we generate docs doesn't support the Base API, and requires the old Cop API. I've updated it to the legacy approach to correction, and will open an issue to migrate.

[KaanOzkan]

I like the cop 👍 . You have a CI failure on Ruby 3+

[sambostock]

Switched to positional arguments. I'll squash commits when I'm back at my computer.

What do you think of the offense message/docs?

[paracycle]

Small wording change to better emphasize which apps should use the cop.

[andyw8]

(for anyone else wondering: this is patched by shopify-types).

[vinistock]

I actually want to release the next version for a recent fix. Can we set this to 0.7.0 already?

[sambostock]

I assume Rubocop proper has tooling that does this automatically during the release process, but we haven't copied their tooling exactly (see #132). I think the expected workflow would be for the PR that bumps the version to do a find and replace of <<next>> with whatever version it's bumping the gem to.